The present invention relates to a method and apparatus for truing crankshafts and, more particularly, to a method and apparatus for the fast and cost effective truing of crankshafts during the manufacture or reassembling of pressed-together multi-cylinder engine crankshafts. Specifically, the invention relates to a novel technique and tool for truing the crankshafts used in personal watercraft and snowmobile engines, as well as certain outboard engines and other multi-cylinder two-stroke engines.
Crankshafts for precision machines must be accurately manufactured, or reassembled, to properly drive the engine components of the machines of which they are part. Methods and tools used in the manufacture of crankshafts are described in U. S. Pat. Nos. 4,979,335, 5,625,945 and 5,984,599. A most important aspect of such accurate manufacturing, or reassembling, is the truing of the crankshafts. A crankshaft is often comprised of multiple crankshaft sections, and each of these sections usually consists of two xe2x80x9cjournalsxe2x80x9d, connected by a center pin, and one or more associated bearings. A xe2x80x9cjournalxe2x80x9d is an annular disc, or xe2x80x9cwebxe2x80x9d, with a peripheral pin transversely attached to it. A xe2x80x9cconnecting rodxe2x80x9d, attached to the peripheral pin, connects the crankshaft to the corresponding piston of the engine of which the crankshaft is part. When a crankshaft is comprised of multiple crankshaft sections, xe2x80x9ctruingxe2x80x9d refers to the straightening of the crankshaft, whose sections are out of alignment with respect to the crankshaft""s axis of rotation, by pinching, hammering, wedging or otherwise applying a force or forces on the components of the sections so as to realign the components until the distortion of the crankshaft is minimized or eliminated. Uncorrected distortions will tend to cause misalignment of the main bearings, crankpins and other components of the crankshaft sections and result in a distorted crankshaft, that is, one that wobbles. These deviations from the true running of the crankshaft sections, with respect to the axis of rotation of the crankshaft, are remedied by the truing, or straightening, operation. Proper truing of the crankshafts is particularly critical when the crankshafts are xe2x80x9cpressed-together crankshaftsxe2x80x9d, that is, crankshafts used in multi-cylinder engines where the connecting center pins of at least some of the sections are press fit to one or both of the journals to which they are connected. Press fitting is the assembling of any two machined pieces by creating a bond between them as a result of the fact that one of them has been inserted within the other, so as to be properly in place, by the use of force. For example, a round connecting center pin may be press fit to a journal by providing, in the journal, an orifice with a diameter between 0.0002 and 0.004 inches smaller than the diameter of the pin, and forcing the pin into the orifice by mechanical exertion. Pressed-together crankshafts for multi-cylinder engines are built and reassembled by manufacturers and rebuilders such as Kawasaki, Polaris, Yamaha and others for combustion engines with several cylinders and, in particular, for combustion engines for personal motorized watercrafts, snowmobiles and similar vehicles. In contrast to pressed-together crankshafts, xe2x80x9csingle-piece crankshaftsxe2x80x9d are designed so that the journals and connecting center pins form one solid single piece, and, since the crankshafts themselves are forged in one piece, the connecting rods and the bearings are designed so that they may be replaced and/or serviced while the crankshaft remains in one piece. As a result, single-piece crankshafts cannot be disassembled and reassembled, and, consequently, the crankshaft truing techniques for single-piece crankshafts are different from the crankshaft truing techniques for pressed-together crankshafts, and normally involve bending and compressing the one-piece crankshaft until it runs true on one axis of rotation. Pressed-together crankshafts, on the other hand, must be disassembled and reassembled whenever their bearings fail, or when their connecting rods wear or break due to extended use. Otherwise, the engines do not operate properly, or simply stop running, unless the crankshafts are taken apart and reassembled, aligned and trued. Also, pressed-together crankshafts often have to be taken apart to replace defective bearings and to perform repairs or maintenance. When taken apart, these crankshafts always fall out of tolerance and have to be re-aligned and re-trued.
Techniques for truing, or straightening, workpieces such as crankshafts are described in U.S. Pat. Nos. 4,517,717, 4,860,566, 5,001,917, 5,235,838 and 5,333,480. Most of these techniques are concerned with single-piece crankshafts, and they involve bending, flexing, hard rolling and the like, by themselves or in combination; but such techniques do not allow an operator to determine the degree of distortion and perform the necessary straightening correction on a pressed-together multi-cylinder-engine crankshaft without having to remove the crankshaft from the work station. Removing a pressed-together multi-cylinder-engine crankshaft from the work station is time consuming, adds an extra step, in which the probability of human and/or machine error increases, and contributes additional and unnecessary cost to the truing operation. Conventional crankshaft truing techniques can be cumbersome and time-consuming, and add substantial costs to the building and reassembling of crankshafts, particularly when the crankshafts are pressed-together crankshafts. It is apparent, then, that a need exists to provide a technique and a tool for properly and quickly truing crankshafts, and, in particular, for properly and quickly truing pressed-together multi-cylinder-engine crankshafts in minimum time and with minimum expense.
An object of this invention is to provide a technique and a tool for accurately truing crankshafts. An object of the instant invention is also to provide a method and an apparatus for accurately and rapidly truing pressed-together crankshafts, which method and apparatus may be used on practically all kinds of pressed-together crankshafts regardless of their make or origin. Another object of the invention is to provide an inexpensive method and apparatus for properly truing the pressed-together crankshafts normally found in the multiple-cylinder combustion engines used in personal watercrafts and snowmobiles, as well as in other multiple-cylinder outboard engines.
A further object of this invention is to provide a method and a tool for the accurate, rapid and inexpensive truing of said crankshafts that can be used and operated by essentially one operator with minimum amount of training and which allows the operator to detect and measure the degree of distortion and perform the required correction while the crankshafts remain on the work station, that is, without having to remove the crankshafts from the work station. These and other objects of the invention will become apparent from the disclosure that follows.
The above objects are achieved by the truing tool and method of the instant invention. When used properly and in accordance with the method disclosed herein, the truing tool, or apparatus, of this invention allows one single operator to accurately determine the existence, location and degree of distortion and then proceed to straighten and assemble pressed-together crankshafts in minimum time and with minimum expense.
The truing tool, or apparatus, of this invention comprises a supporting base, a set of lockable holding means, a movable shelf, a cam-operated lever, sliding position detection means, and a top-mounted clamp. When assembled in the manner provided herein, the apparatus provides the means for holding the crankshaft to be trued in a xe2x80x9cmeasuring positionxe2x80x9d, that is, in a position with respect to the work or assembly station where an operator may detect, locate and measure the degree of distortion and decide if, where and how much force to apply to the crankshaft in order to straighten it. The truing tool of this invention also provides the means for holding the crankshaft in a xe2x80x9ctruing positionxe2x80x9d, that is, in a position with respect to the work or assembly station where an operator may then proceed to apply the forces necessary to effect the straightening of the crankshaft, all without removing the crankshaft from the work or assembly station and while allowing the operator to switch back and forth from the measuring position to the truing position as often as necessary or desirable.
The supporting base comprises a rigid plate, preferably made of steel, provided with multiple openings strategically located to receive parts of the other components of the truing tool and to secure the base to a worktable or bench. The front edge of the supporting base is provided with orifices for mounting the cam-operated lever at a convenient location along the edge. The base is preferably equipped with at least two rigid members, parallel to each other and transversally located with respect to the surface of the supporting base and provided with means for accepting and coupling with the hinging means of the movable shelf, as more particularly set forth below.
The set of lockable holding means comprises one movable support block and two companion stationary support blocks, each such block provided with one or more openings adapted to receive one or more bolts or other means for securing the blocks, and shaped as to allow the blocks to receive and hold the crankshaft to be trued. The movable support block is provided with one or more openings at the bottom to allow it to be locked to the movable shelf and hinge up and down with respect to the surface of the supporting base when the movable shelf is driven by the cam-operated lever, as more particularly set forth below. The movable support block is flanked by the two companion support blocks, which are stationary. For convenience, the movable support block is sometimes referred to in this description as the xe2x80x9cinner support blockxe2x80x9d, and the two companion stationary support blocks are sometimes referred to as the xe2x80x9couter support blocksxe2x80x9d. The three support blocks are preferably made of steel, and are preferably V shaped, but they may be made of any other rigid metal or material and shaped in any other configuration or form that will allow the blocks to receive and hold the crankshaft to be trued. The inner support block is located and sized to receive and hold the bearings of the crankshaft when the truing tool is in the measuring position. The two outer support blocks are located and sized to receive and hold the crankshaft journals when the truing tool is in the truing position.
The movable shelf comprises an L-shape rigid member provided with a through rod or other means for hinging up and down with respect to the surface of the supporting base when driven by the cam-operated lever. The movable shelf is also provided with at least one orifice capable of accepting a screw, or similar means, for locking the shelf to the inner support block. Preferably, the bottom of the movable shelf is provided with a recessed groove sized to receive and hold in place the push rod of the cam-operated lever.
The cam-operated lever comprises lever means, attachable to the supporting base, for raising and lowering the movable shelf and the inner support block of the set of lockable holding means. Preferably, the cam-operated lever is a manually operated, two-position lever provided with a cam mechanism by which a handle may transfer movement to a fixed-travel push rod. The cam-operated lever is attached to the front edge of the supporting base by means of bolts, screws or any other suitable hardware. Preferably, steel screws sized to match the orifices provided on the front edge of the supporting base are used to secure the lever to the supporting base. The cam-operated lever is so located on the front edge of the supporting base as to allow its push rod to exert pressure on the recessed groove of the movable shelf and cause the shelf to hinge upwards and away from the supporting base when the handle of the cam-operated lever is moved to the up position.
The sliding position detection means comprise a plurality of position detectors mounted on sliding holders, strategically located and capable of moving over and retrieving from the surface of the crankshaft to be trued. The position detectors provide an out-of-tolerance indication of the positions of the crankshaft sections with respect to the rotational axis of the crankshaft. The position detectors may be conventional detectors of the type that include a feeler rod whose lower end bears on the crankshaft being trued and whose upper end is connected to a dial that displays the degree of distortion of the crankshaft.
The top-mounted clamp comprises hinged mechanical means for compressing and firmly holding the crankshaft to be trued. The top-mounted clamp is preferably mounted on the end of the movable shelf opposite the end on which the push rod of the cam-operated lever exerts pressure, so that the clamp moves with and whenever the shelf is made to hinge with respect to the surface of the supporting base. The top-mounted clamp is also preferably provided with its own independent mechanism for manually causing the clamp to hinge with respect to its mount on the movable shelf and be locked in an inactive or xe2x80x9cupxe2x80x9d position and a clamping or xe2x80x9cdownxe2x80x9d position. Preferably, the clamp is provided with a set of adjustable rubber stoppers or similar adjustable means for improving the grip of the clamp on the surfaces with which it is made to come into contact. Such preferred means for improving the grip of the clamp are positioned on the clamp and sized so as to allow them to come into contact with the bearings of the crankshaft being trued and exert sufficient pressure on them to maintain the bearings firmly in position and keep the crankshaft from falling off or slipping.
In truing a crankshaft, an inner support block is chosen in accordance with the width and diameter of the bearings of the crankshaft which is to be trued. Thus, an inner support block is selected whose distance between its two parallel walls is long enough to accommodate the width of the bearings and short enough to provide a snug fit between the width of the bearings and the space created between the two walls, and whose depth and V opening are long enough and wide enough, respectively, to clear the diameter of the bearings. The width of the walls of the inner supporting block is not critical: the walls simply should be wide enough to provide structural integrity to this component of the invention. The two outer supporting blocks are chosen in accordance with the dimensions of the journals of the crankshaft which is to be trued. Thus, outer support blocks are selected whose depths and V openings are long enough and wide enough, respectively, to clear the diameter, or other applicable space defining dimension, of the journal webs. In addition, the walls of the outer supporting blocks should be wide enough to accommodate the webs, but not so wide as to interfere with the normal rotation of the connecting rod of the crankshaft. The movable shelf and the three support blocks are then placed on the supporting base so that the inner support block rests on the movable shelf and the two outer support blocks flank the movable shelf and the inner support block. The bottom of the inner support block is then attached to the top of the movable shelf by means of bolts or other suitable hardware, and the two outer support blocks and the movable shelf are attached to the base, also by means of bolts or other suitable hardware. The handle of the cam-operated lever is actuated to cause the lever push rod to move to the up position thereby pushing the movable shelf and the inner support block away from the surface of the supporting base and into the truing tool measuring position. The position detection means are slid forward towards the front edge of the supporting base and into the measuring position, and the independent mechanism of the top-mounted clamp is activated to cause the clamp to come down over the inner support block and hold the crankshaft in place for measuring. By bringing the position detection means in contact with the crankshaft at various strategic places on the crankshaft, the operator is able to determine the location and degree of distortion, or out-of-tolerance, of the workpiece, and decide how to carry out the necessary straightening correction. The operator then proceeds to change to the truing, or working, position. This is accomplished by first moving the handle of the cam-operated lever to cause the lever push rod to move to the down position, thereby pulling, or releasing, the movable shelf and the inner support block back to the surface of the supporting base, and then sliding the position detection means towards the back of the supporting base, while lifting and releasing the top-mounted clamp. The operator may then pinch, wedge, hit and/or take any other action required or desirable to straighten the crankshaft. The measuring and straightening cycle may be repeated once, or several times, until the desired truing of the crankshaft has been achieved.